Tuesday, September 11, 2012

Cassini Space Probe Update

Today I'll post an update about the space probe, Cassini. Posing for portraits for NASA's Cassini spacecraft, Saturn and its largest moon, Titan, show spectacular colors in a quartet of images being released today. One image captures the changing hues of Saturn’s northern and southern hemispheres as they pass from one season to the next.

A wide-angle view in today’s package captures Titan passing in front of Saturn, as well as the planet’s changing colors. Upon Cassini’s arrival at Saturn eight years ago, Saturn’s northern winter hemisphere was an azure blue. Now that winter is encroaching on the planet’s southern hemisphere and summer on the north, the color scheme is reversing: blue is tinting the southern atmosphere and is fading from the north.

The image below shows the newly discovered south polar vortex in the atmosphere of Titan, reported recently by Cassini scientists. Cassini's visible-light cameras have seen a concentration of yellowish haze in the detached haze layer at the south pole of Titan since at least March 27. Cassini's visual and infrared mapping spectrometer spotted the massing of clouds around the south pole as early as May 22 in infrared wavelengths. After a June 27 flyby of the moon, Cassini released a dramatic image and movie showing the vortex rotating faster than the moon's rotation period.

These new images became possible because Cassini's newly inclined -- or tilted -- orbits allow more direct viewing of the polar regions of Saturn and its moons.

The image below shows a close up of the concentration of high-altitude haze and a vortex materializing at the south pole of Saturn’s moon Titan, signs that the seasons are turning on Saturn’s largest moon. The structure inside the vortex is reminiscent of the open cellular convection that is often seen over Earth's oceans. But unlike on Earth, where such layers are just above the surface, this one is at very high altitude, maybe a response of Titan's stratosphere to seasonal cooling as southern winter approaches.

Cassini first saw a “hood” of high-altitude haze and a vortex, which is a mass of swirling gas around the pole in the moon’s atmosphere, at Titan’s north pole when the spacecraft first arrived in the Saturn system in 2004. At the time, it was northern winter. Multiple instruments have been keeping an eye on the Titan atmosphere above the south pole for signs of the coming southern winter.

While the northern hood has remained, the circulation in the upper atmosphere has been moving from the illuminated north pole to the cooling south pole. This movement appears to be causing downwellings over the south pole and the formation of high-altitude haze and a vortex.

Scientists are looking forward to seeing more of the same -- new phenomena like Titan’s south polar vortex and changes wrought by the passage of time and seasons -- during the remainder of Cassini’s mission.

Cassini has been in orbit now for the last eight years, and despite the fact that we can’t know exactly what the next five years will show us, we can be certain that we will continue to be amazed by the images. Launched in 1997, Cassini went into orbit around Saturn on July 1, 2004. It is in its second mission extension, known as the Solstice Mission, and one of its main goals is to analyze seasonal changes in the Saturn system.

The next image is an unusual angle showing the moon, Titan, on the other side of some of Saturn's rings.

Here is a view of Titan from the back side showing its outer colors...

It's been nearly two years since NASA's Cassini spacecraft has had views like that shown in a recent picture (see below) of Saturn's glorious rings. These views are possible again because Cassini has changed the angle at which it orbits Saturn and regularly passes above and below Saturn's equatorial plane. Steeply inclined orbits around the Saturn system also allow scientists to get better views of the poles and atmosphere of Saturn and its moons.

Below is a NASA artist's concept of a close-up view of Saturn's ring particles. The planet Saturn is seen in the background (yellow and brown). The particles (blue) are composed mostly of ice, but are not uniform. They clump together to form elongated, curved aggregates, continually forming and dispersing. The space between the clumps is mostly empty. The largest individual particles shown are a few meters (yards) across.

Two sets of measurements made by NASA's Cassini spacecraft in the ultraviolet and infrared ranges of radiation have provided new insights into the behavior and make-up of Saturn’s ring particles. Researchers using Cassini’s ultraviolet imaging spectrograph have shown that the processes that form temporary clumps of particles and then destroy them are driven by the gravity of some of Saturn’s moons. The numbers of large and small clumps appear to follow what in biology is called a “predator-prey relationship” that governs, for example, the numbers of foxes and hares in an area. Researchers using Cassini’s composite infrared spectrometer and theoretical models have also characterized the sizes, speeds of rotation and the "surface densities" of particles in different zones of the rings.


Saturn was playing the lightning storm blues. NASA’s Cassini spacecraft has captured images of last year’s storm on Saturn, the largest storm seen up-close at the planet, with bluish spots in the middle of swirling clouds. Those bluish spots indicate flashes of lightning and mark the first time scientists have detected lightning in visible wavelengths on the side of Saturn illuminated by the sun. What scientists do know is that the intensity of the flash is comparable to the strongest flashes on Earth. The visible energy alone is estimated to be about 3 billion watts lasting for one second. The flash is approximately 100 miles (200 kilometers) in diameter when it exits the tops of the clouds. From this, scientists deduce that the lightning bolts originate in the clouds deeper down in Saturn’s atmosphere where water droplets freeze. This is analogous to where lightning is created in Earth’s atmosphere.

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